This invention relates to a method for removing bitumen from tar sands. In another aspect, this invention relates to a method for removing bitumen from tar sands by solvent extraction. In another aspect, this invention relates to a method of removing bitumen from tar sands by extraction with an aromatic hydrocarbon solvent. In still another aspect, this invention relates to the removal of sand fines from a solvent-bitumen extract. In still another aspect, this invention relates to the removal of sand fines from a solvent-bitumen extract by washing said extract with water containing a cationic surfactant. In still another aspect, this invention relates to a method of removing bitumen from tar sands by solvent extraction wherein sand fines are removed from the solvent-bitumen extract by washing with water containing a cationic surfactant.
Various methods have been proposed in the past for the recovery of bitumen from tar sands. One such method utilizes the technique of solvent extraction. A serious problem, however, in using a solvent extraction process to remove bitumen from tar sands is that sand fines, primarily particles less than 50 microns in diameter, are carried over in the solvent-bitumen extract. The presence of the sand fines and the failure to remove the sand fines result in a high-ash bitumen product as well as problems with plugging of equipment used in the separation process, e.g., especially filtration equipment. Removal of the sand fines is, therefore, important in providing a desirable low-ash bitumen product and minimizing fouling and plugging of equipment used in the process.
Various methods have been proposed to solve the problem caused by the presence of the sand fines. The results are not entirely satisfactory, however, as far as economics and practicality are concerned.
U.S. Pat. No. 3,117,922 discloses a method in which tar sand and solvent are generally slurried so as not to break the water film that is thought to surround the fine sand particles. This process requires a multi-solvent system, however, and would not be practical for tar sands in which the water had previously been removed or dried out.
Other methods have proposed an elaborate system of staged cyclones, centrifuges, and vacuum filters. After removal of coarse sand from a bitumen-solvent solution, if one attempts to filter the bitumen-solvent extract without centrifuging, the filter is blocked immediately due to the fine sands present in the solution. Even after extensive centrifuging and filtration, however, the bitumen-solvent solution still contains fine sands which amount to about 0.5 to 1.0 weight percent of the dissolved bitumen. Furthermore, an elaborate system of cyclones, centrifuges, and vacuum filters is extremely expensive to buy and operate.
U.S. Pat. No. 3,459,653 discloses a process for removing tar from tar sands which comprises slurrying the tar sands and the solvent in the presence of an added amount of water followed by filtration of the slurry and recovery of the solvent from the sand bed. A water wash of the decanted bitumen-solvent solution will permit filtration as disclosed in U.S. Pat. No. 3,459,653, but, this wash will require at least one-half gallon of water per gallon of recovered bitumen. This would cause problems in recovering bitumen since the fines and bitumen residuals would be thoroughly suspended in the water thus resulting in an undesirable, high-ash bitumen product. The process also consumes a great deal of water.
Accordingly, one object of this invention is to provide an improved process for the recovery of bitumen using solvent extraction.
Another object of this invention is to provide a process for recovering a low-ash bitumen product.
Yet another object of this invention is to provide a process for the recovery of bitumen from tar sands in which fouling and plugging of equipment used in the process is minimized.
Another object of this invention is to provide a process for the recovery of bitumen which reduces water consumption and has little solvent loss.
Other objects, aspects, and the several advantages of this invention will be apparent to those skilled in the art upon a study of this disclosure, the appended claims, and the drawing.